1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine or a printer that transfers a toner image formed on an image bearing member by an electrophotographic process to a transfer material, and then fixes the toner image to obtain a fixed image on the transfer material.
2. Description of the Related Art
There has been well known an electrophotographic image forming apparatus that includes a process of transferring a toner image formed on a surface of an image bearing member to a transfer material such as paper. A color image forming apparatus generally employs a configuration in which multiple photosensitive members are arranged in line so that toner images are sequentially formed by the respective photosensitive members and are transferred to a transfer material directly or via an intermediate transfer member.
Recent diversification of printer demands has been accompanied by a rise in request for non-margin printing in the color image forming apparatus in particular. There has conventionally been known a method in which a transfer material slightly larger than an image is used and margins thereof are cut after printing. To eliminate the cutting work, there is an increasing need for so-called non-margin printing, in which an image is printed on an entire surface of the transfer material without forming any margins on the edges of the transfer material beforehand.
For an ink-jet type of an image forming apparatus, an apparatus with a non-margin printing function has been brought to the market. Such an apparatus is disclosed in, for example, Japanese Patent Application Laid-Open No. H10-337886.
In an attempt to realize an electrophotographic full-color image forming apparatus that supports non-margin printing, there arises the following technical problem.
The toner image present in the edge portions of the transfer material is fixed under a condition different from that of the toner image in the conventional margin printing, and hence when the fixing operation is performed under the same condition, there is a fear that the obtained fixed image is not uniform and image contamination (hot offset) occurs because of fixing failure or excessive heating. In a case where the image contamination is prevented, there is a demand that image quality be maintained as high as possible.